A US appeals court on Wednesday considered whether Oracle should be afforded copyright protection over certain portions of the Java programming language in a case that is being closely watched by software developers.

The appeal, being heard by the US Court of Appeals for the Federal Circuit in Washington, DC, is the latest chapter in the company's long-running patent and copyright battle over Google's use of Java application programming interfaces (APIs) in Android. Oracle sued Google in 2010, alleging that Google's use of 37 Java APIs in its mobile operating system constituted patent and copyright infringement.

Google argued it was free to use them because the Java programming language is free to use and the APIs are required to use the language. Oracle countered that Google knowingly used the APIs without a license from Sun Microsystems, which Oracle purchased in 2010.

While a jury handed down a partial victory in May 2012 that found that Google infringed the overall structure, sequence, and organization of Java's language, Judge William Alsup later ruled that the APIs were noncopyrightable, leading to the dismissal of Oracle's copyright infringement claim, which Oracle appealed.

In its appeal, Oracle argued that Google "took the most important, the most appealing" parts of the APIs to create Android.

"Google took the code for its own uses, and it did it to leverage Oracle's fan base," Oracle lawyer Josh Rosenkranz said. "Google was very careful to only use what was structural. No one was able to use the Java language as a smartphone platform."

During Wednesday's hearing, the three-judge panel's questioning suggested it was leaning toward Oracle's position, according to a Bloomberg account of the proceedings. Federal Circuit Judge Kathleen O'Malley questioned whether Alsup's ruling meant Google was free to use APIs developed by Apple and Microsoft.

"Yes, but only the command structure," Google attorney Robert Van Nest told the court. "They would have to rewrite millions of lines of code. That's what Android did -- 15 million lines of Android code are all original."

Meanwhile, O'Malley and Judge Richard Taranto said two of the key legal precedents cited by Google were not relevant to whether the Java APIs could be copyrighted, Reuters reported.

The appeals court, which is hearing the case because Oracle had also claimed patent infringement, isn't expected to issue a decision for months.

Correction at 6:35 a.m. December 5:An indirect quote from Federal Circuit Judge Kathleen O'Malley has been corrected. She questioned whether a prior ruling meant that Google was free to use APIs developed by Apple and Microsoft.